RT 205 Electromagnetism II

Question 1

Faraday’s Law: Methods to induce a current:

1. Moving a permanent magnet into and out of a coil of wire also induced a current in the wire while the magnet was in motion.
2. Moving a conductor near a stationary permanent magnet caused a current to flow in the wire, too, as it was moving.
3. Made it possible to determine the direction of the induced current flow.

Answer 1

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Question 2

Four factors of Faraday’s Law: The magnitude of the induced current depends on four factors.

Answer 2

1. The strength of the magnetic field
2. The velocity of the magnetic field as it moves past the conductor
3. The angle of the conductor to magnetic field (lines of flux)
4. The number of turns in the conductor

Question 3

Lenz’s Law
An induced emf generates a current that induces a counter magnetic field that opposes the magnetic field generating the current. Name the law.

Answer 3

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Question 4

The production of an electromotive force (emf) or voltage in an electric circuit caused by a changing magnetic flux in a neighboring circuit

Answer 4

Mutual Induction

Question 5

Property whereby an electromotive force is induced in a circuit by a variation of current in the circuit itself

Answer 5

Self Induction

Question 6

Opposition to the flow of AC current produced by an inductor; measured in ohms and varies in direct proportion to frequency

Answer 6

Inductive Reactance

Question 7

Fleming’s Right Hand Generator Rules
Thumb: points in direction of conductor (armature) moves
Index finger: points in the direction of magnetic lines of force
Middle finger: Indicates the direction of conventional current flow

Answer 7

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Question 8

Converts mechanical energy into electrical energy

Answer 8

Dynamo (Generator)

Question 9

How is electricity produced in a dynamo?

Answer 9

From magnets whirling inside of coils of wire in the generator core.

Question 10

Components of a Generator
Moving part of magnetic device consisting of one or more coils that are electrically connected to create a rotational section of a generator

Answer 10

Armature (Conductor)

Question 11

Components of a Generator

Means of producing an electrical connection through a rotational assembly

Answer 11

Slip Rings

Question 12

Components of a Generator

Conducts current between rotating stationary parts of a generator or motor

Answer 12

Brushes

Question 13

Produced when wires motion relative to the lines of force is reversed

Answer 13

Alternating Current

Question 14

1 Cycles per second (cps)= 1 Hz

Answer 14

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Question 15

U.S. Generators utilize how many Hertz?

Answer 15

60 Hz (or 120 Changes per second)

Question 16

Components of a Generator
A single ring that is divided in half, with each half connected to one end of the armature wire (Replaces pair of slip rings, produced direct current, keep current flowing in the same direction)

Answer 16

Commutator Ring

Question 17

Converts electrical to mechanical energy

Answer 17

Motors

Question 18

Fleming’s Left Hand Motor Rule
Thumb: Movement of Conductor on Rotor
Index: Magnetic lines of force field
Middle: Current or electron flow

Answer 18

Blank

Question 19

What type of rings do AC motors use?

Answer 19

Slip Rings

Question 20

What type of rings do DC motors use?

Answer 20

Commutator rings

Question 21

Types of motors
Synchronus Induction
Induction motor electromagnets that turn the anode; Supplied with multiphase current

Answer 21

Stator

Question 22

Types of motors
Synchronus Induction
A hollow copper cyclinder or cuff that is attached to the anode disk by a molybdenum shaft (Used in rotating anode x-ray tubes)

Answer 22

Rotor

Question 23

Measures Direct Current (Use permanent magnets)

Answer 23

Galvanometers

Question 24

Measures Alternating Current (Use electromagnets)

Answer 24

Ammeter

Question 25

Measures connected in parallel (Measure potential difference)

Answer 25

Voltmeter

Question 26

A device in which two coils are placed near one another without electrical connection (The number of turns in the coils differs, causing a change in current in the secondary coil; Serves to either increase or decrease the voltage)

Answer 26

Transformers

Question 27

Three causes of loss of efficiency in transformers: First cause:Copper loss (I^2R loss) 1. Resistance in the wires (minimized by using low resistance wire. 2. Large diameter copper (Minimized by using high voltage and low amperage)

Answer 27

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Question 28

Three causes of loss of efficiency in transformers: Second cause: Hysteresis loss (lagging loss) 1. Results from energy expended as the continually changing AC current magnetizes, demagnetizes, and remagnetizes the core

Answer 28

Blank

Question 29

Three causes of loss of efficiency in transformers: Third cause: Eddy current loss 1. Currents that oppose the magnetic field that induced them (laminating the core reduces this loss)

Answer 29

Blank

Question 30

Accumulates and stores an electrical charge (Two oppositely charged metal plated separated by dielectric)

Answer 30

Capacitors

Question 31

A material that can sustain an electric field but does not conduct electric current

Answer 31

Dielectric

Question 32

``` Capacitor Formula: C= Q/V C= capacitance of the capacitor Q= charge on one of the plates of the capacitor V= voltage across the capacitor ```

Answer 32

Blank

Question 33

What is capacitance measure in?

Answer 33

farads (F)

Question 34

1F= 1Coulomb/Colt | This means how many coulombs of charge can be stored in a capacitor per volt in the power source

Answer 34

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Question 35

The process of converting alternating current into a unidirectional current, by removing or inverting that part of the wave laying on one side of the zero amplitude axis

Answer 35

Rectification

Question 36

A solid-state switching device for semiconductors to convert AC current in one of two directions controlled by an electrode (Thyristor or silicon-controlled rectifier (SCR))

Answer 36

Solid-state diodes

Question 37

A device that allows current to flow in one direction only (Produced by sandwiching n-type and p-type crystals

Answer 37

Diode

Question 38

A cathode and anode separated so that electrons can only flow from cathode to anode

Answer 38

Vacuum tube type diode

Question 39

Flow of electrons from a metal or metal oxide surface, caused by thermal vibrational energy overcoming the electrostatic forces holding electrons to the surface. The effect increases dramatically with increasing temperature (1000- 3000 K)

Answer 39

Thermionic Emmission

Question 40

Another name for Thermionic emission?

Answer 40

Space charge cloud

Question 41

Protects from current that can damage equipment?

Answer 41

Rectification

Question 42

Rectifying process | Passes only one-half of each incoming sinusoid, and does not pass the opposite half cycle

Answer 42

Half-wave Rectification

Question 43

Rectifying process Passes the positive half and inverts the negative half cycle of the input sinusoid so that the output contains two half sine pulses for each input cycle

Answer 43

Full-wave Rectification

Question 44

Main Circuit Parts of an x-ray machine: | The switch that generates the power to the x-ray tube

Answer 44

Main Switch

Question 45

Main Circuit Parts of an x-ray machine: | A remote control device that permits current flow through the circuit

Answer 45

Exposure Switch

Question 46

Main Circuit Parts of an x-ray machine: | Device used to end the exposure at an accurately measured preset time

Answer 46

Timer

Question 47

Main Circuit Parts of an x-ray machine: | Where the alternating current comes form to power the circuit

Answer 47

Main breaker

Question 48

Main Circuit Parts of an x-ray machine: | This is where you adjust the kVp for the exposure

Answer 48

Autotransformer

Question 49

Main Circuit Parts of an x-ray machine: This transformer bumps the voltage up so that the x-ray tube has very high voltage to make the electrons have enough energy to form x-rays

Answer 49

High-voltage step-up transformer

Question 50

Main Circuit Parts of an x-ray machine: | This makes the current only go in one direction through the x-ray tube

Answer 50

Four-diode rectification circuit

Question 51

Main Circuit Parts of an x-ray machine: | This variable resistor adjusts the current going to the filament

Answer 51

Filament circuit variable resistor

Question 52

Main Circuit Parts of an x-ray machine: | This transformer steps the voltage down and therefore the current up.

Answer 52

Filament step-down transformer

Question 53

Main Circuit Parts of an x-ray machine: | This is where the x-rays are created

Answer 53

X-ray tube

Question 54

Main Circuit Parts of an x-ray machine: | This rotates the anode

Answer 54

Rotor Stator